This invention relates to a float operated device which operates at high pressure, such as a pressure powered pump or a condensate trap.
In the context of the present invention, the expression "high pressure" means a pressure in excess of 5 bar and refers to the internal pressure in the housing of the device, to which pressure the float is subjected.
Pressure powered pumps are used in steam systems in order to raise condensate to a condensate return system from which the condensate is reintroduced to the steam generating boiler. Such pumps comprise a chamber in which the condensate accumulates, to be periodically discharged by the periodic admission of steam and venting of the chamber under the control of a float which is responsive to the level of condensate in the chamber. Examples of such pumps are disclosed in GB 2302916 and U.S. Pat. No. 5,141,405.
In some applications, where there is an adequate pressure head at the condensate inlet, the rising float may operate an outlet valve before steam is admitted to the chamber, the condensate then being discharged through the outlet under the pressure at the inlet. If the pressure head is insufficient to discharge the condensate, the float will rise further, and steam will be admitted to the chamber to force the condensate out under pressure.
The pressure powered pump is normally situated at the lowest point in the steam system. It is usually floor-mounted. Sometimes the heat exchanger, or other component of the steam system from which condensate is supplied to the pressure powered pump, is only a small distance above the floor, and consequently the filling head for the pump is too small to produce an adequate filling rate for the pump chamber. It is therefore desirable for the pressure powered pump to operate reliably with a small change in liquid level within the chamber between the end positions of the float. However, in conventional pressure powered pumps which use a spherical float, the diameter of the float itself influences the overall height of the pump chamber. The size of the float itself is dictated by the need to provide adequate buoyancy to operate the toggle mechanism in the rising direction of the float, and adequate weight to operate the toggle mechanism in the reverse direction as the float falls. Spherical floats have conventionally been used in high pressure devices such as pressure powered pumps and condensate traps because a spherical shape is best able to withstand the high pressure to which they are subjected in use.
Another disadvantageous characteristic of known pressure powered pumps is that the toggle mechanism exerts its greatest resistance to movement of the float when the float is at its end positions. This means that substantially the entire buoyancy (or weight) of the float is utilized to overcome the resistance imposed by the toggle mechanism. Consequently, there is no surplus energy which can be utilised to perform other operations, such as the opening of an outlet valve for process fluid.